The present invention relates to a magnetic brush development apparatus for use with an electrophotographic copying machine and an electrostatic recording apparatus.
The magnetic brush development apparatus is an apparatus of the type in which a magnetic developer is supplied to a development sleeve having a magnet therein and a magnetic brush is formed on the development sleeve, and by bringing the magnetic brush into contact with a latent electrostatic image formed on a photoconductor or a recording material, the latent electrostatic image is developed.
With respect to the supply of the developer to the development sleeve in the magnetic development apparatus, two types of the magnetic development apparatuses are known. In one type, the developer is supplied to the development sleeve from a hopper situated above or beside the development sleeve, and in the other type, the developer placed in a lower portion of the development apparatus is attracted to the development sleeve. In both types, the development sleeve transports the developer deposited on the surface of the development sleeve to the photoconductor or to the recording material, with the magnet disposed in the development sleeve or the development sleeve rotated.
As the magnetic developer, a one-component type developer and a two-component type developer are known. The one-component type developer comprises colored particles (toner) containing magnetic powders therein. The two-component type developer comprises magnetic particles called carriers and non-magnetic toner.
In either case, development is effected by the toner being attracted electrostatically to a latent electrostatic image formed on a photoconductor or the recording material. In the case of the two-component type developer, the toner is triboelectrically charged by the carriers to the polarity opposite to that of the latent electrostatic image. In the case of the one-component type developer, when the magnetic toner is low in resistivity, the toner is charged to the polarity opposite to that of a latent electrostatic image as the toner is brought to the latent electrostatic image, but when the magnetic toner is high in resistivity, the toner is triboelectrically charged to the polarity opposite to that of a latent electrostatic image within the container of the toner or while it is transported to the latent electrostatic image.
Since the one-component type magnetic developer does not contain carriers, the concentration control of the developer is unnecessary and the developer is not deteriorated by carriers. Therefore, handling of the one-component type developer is easy. However, when the developer runs out, the image density is reduced so quickly that it is necessary to detect the amount of the remaining developer before the developer runs out.
Conventionally, such detection of the remaining developer is performed by detecting the change of a leaked magnetic flux or the change of an inductance of the developer since they depend upon the quantity of the developer in a detecting portion.
However, the detecting efficiency of the above-mentioned methods is low and an expensive amplification circuit, a comprison circuit, a compensation circuit, and the other circuits are necessary. Furthermore, the above-mentioned methods are not stable in operation, and occasionally, the flow of the developer is hindered by a developer detecting means disposed in the development apparatus.